Microbial denitrification is a frequently used and inexpensive method of removing nitrogenous waste from wastewater. Two common configurations utilize either packed beds (also referred to as fixed film) or fluidized beds. Denitrifying microbial cultures have been supported on a variety of substrates including sand, ceramics, polymers, clay, and gels, to name a few. Fluidized bed denitrification systems offer a cost-effective solution to wastewater treatment, as they are self-adapting and provide a very large reactive surface area for a given volume compared to fixed film-based filtration systems. The primary disadvantage of microbial systems (or bioreactors) is that the organisms require an environment conducive to supporting their metabolic needs. While biological treatment systems can be flexible and robust, temperature, pH, oxygen content, and contaminant levels are variables to be controlled for optimum performance. Despite this requirement, microbial denitrification is still a cost effective way to treat wastewater.
Such systems can, and typically are, used in conjunction with other wastewater unit processes to achieve acceptable levels of biological oxygen demand (BOD) and/or the removal of other pollutants including, but not limited to, phosphorus, nitrogen, heavy metals, miscellaneous solids, and toxic organics.
The U.S. Department of Agriculture (USDA) and the U.S. Environmental Protection Agency (EPA) promulgate regulations that require entities generating wastewater to confine the discharge to permissible levels. Examples of regulated materials and chemicals included in discharged wastewater are ammonia, phosphates, nitrates, nitrites, and heavy metals. Typically, entities generating wastewater create holding ponds at their site. These ponds can be part of the treatment system and act as storage structures for the wastewater before, during, and after processing. Some processes allow the entities to either discharge their effluent to local waterways, others recycle the treated water by reusing it, for example, for cleaning or irrigation. Addition of wastewater treatment systems prior to these holding facilities can reduce the size required for these holding ponds.
Various entities spend millions of dollars annually to treat their wastewater. The cost of discharging untreated water to a municipal wastewater treatment facility can be prohibitive. In addition, every dollar spent on such discharge could have been spent on other, more beneficial, endeavors, including, for example, improvements to facilities.
Some existing denitrification filters may use a fluidized bed bioreactor having an inverted cone shape. Such a configuration optimizes the active volume of the bioreactor and reduces the volume and pumping requirements for any given throughput due to the high velocity of the liquid at the small part of the cone relative to the average liquid velocity of the entire vessel. An exemplary configuration of a fluidized bed reactor is shown in FIG. 1. In this filter, wastewater W is injected through the top of the filter element through a pipe that discharges at the base of the fluidized bed reactor. In FIGS. 1 and 2, the exemplary filter 100 can receive water to be treated W from either of two input bulkheads 110. Passing through horizontal fill pipes 120, the water W enters a vertical injector pipe 130 and exits out ports 140 adjacent the lowermost end of the vertical injector pipe 130 into the interior 102 of the filter body. Accordingly, the high-pressure stream of water W is forced upwards through the column of bed material 150, e.g., sand (not shown but indicated by dotted underline), which material 150 fills a lowermost portion of the filter's interior (for example, up to fill line 160 when dry). As the water W mixes with the bed material 150, it creates a fluidized bed having an upper boundary above fill line 160. A cone-shaped filter maximizes the efficiency of the fluidization within the column of the fluidized bed. An ideal fluidized bed reactor is one where the entire volume of the bed material becomes fluidized. Cone shaped fluidized beds (compared to straight cylinders) are more tolerant of variations in flow rates and media size uniformity that can lead to media washout in cylinders. It is beneficial if this filter system design is self-leveling and has a built-in overflow capability. To function best, however, a fluidized bed's long axis should be oriented as close to vertical as possible.
In FIGS. 1 and 2, if the filter uses standard 3-inch diameter plumbing, for example, then standard 3-inch parts can be used. At the top of the plumbing, a 3-inch DWV clean out 200 can be connected to a 3-inch cross 202. The horizontal fill pipes 120 can comprise a pair of 3-inch by 7.25-inch sch-160 PVC fittings each on opposing sides of the cross 202 with each being connected to one of a pair of 3-inch by 20.5-inch sch-160 PVC fittings through a 3-inch compression coupling 204. Each of the horizontal fill pipes 120 can be terminated by one of the two input bulkheads 110. The hatched areas of the pipes connected to the cross 202 illustrate the cement joints of the respective pipes. The vertical injector pipe 130 can be a 3-inch by 89-inch sch-160 PVC pipe that is terminated at the bottom thereof by a 4-inch bulkhead 206 holding a 3-inch drain gate 208, a 4-inch by 2-inch bushing 210, and, finally, a 2-inch plug 212. In this exemplary embodiment, four 1.5-inch holes, 2.5-inches on center are at the lower end of the vertical injector pipe 130.
An exemplary diagram for a denitrification process flow that can use a fluidized bed reactor 100 is provided in FIG. 3. Effluent wastewater W is introduced into a set 300 of sumps and filters that are configured in series because microbial reduction of ammonia in an influent stream is a multi-stage process. In a first stage 310, ammonia (NH3) is converted to nitrate (NO3) in the presence of oxygen, an aerobic process called nitrification. Oxygen can be added either as O2 or as a constituent of air. Nitrates are as problematic as ammonia as a contaminant in waste streams. Accordingly, they must be treated as well. As such, in a second stage 320, nitrates are converted to atmospheric nitrogen (N2) in an anaerobic process called denitrification. The number of aerobic and anaerobic filters in any given system is not fixed, but rather depends on the nature of the wastewater being treated and the desired characteristics of the system effluent. FIG. 3 shows a configuration where the first aerobic stage is succeeded by two anaerobic stages. As shown in FIG. 3, the influent W is discharged into an aerobic sump 312 where air 330, for example, is injected to maintain an adequate oxygen concentration sufficient for the aerobic microbes in the ammonia reduction stage of the process. This aerated water is recirculated through a first set of two fluidized bed reactors 314. Aerobically treated water W1 from the aerobic sump 312 then flows to the first of two series-connected anaerobic sumps 322, 324. A second set of two fluidized bed reactors 326 recirculate influent water W1 within a first anaerobic sump 322, which discharges partially treated water W2 to a second anaerobic sump 324, at which a third set of two fluidized bed reactors 328 recirculate fluid therein. Denitrified water W3 flows out of the second anaerobic sump 324 to a final sump 340, where any number of secondary removal systems 350 can be present. For example, if another pollutant is to be removed, then a secondary removal system 350 can be used. Treated water W4 from this final sump 340 can then either be recycled or discharged. Possible direction of the treated water W4 can be to a storage pond, a natural water body, and/or to a wastewater treatment facility as desired. Each of the sumps 312, 322, 324 can be accommodated to fit the needs of a particular facility.
The basic chemical process for treatment of the liquid in the first stage 310 involves aerating a stream of ammonia-rich wastewater and introducing this wastewater to an aerobic sand filter(s) where it first contacts an aerated zone. Here, the ammonia is converted to NO3 as set forth in the following equation:NH4+2O2→NO3−+2H++H2O.Then, the nitrate-rich effluent of the first stage 310 enters at least one anoxic filter where a high density of denitrifying bacteria converts the nitrate to N2 as set forth in the following equation:NO3−+Carbon Source→N2+CO2+H2O+Biomass.
This two-step process is represented in the schematic flow diagram of FIG. 4, which also includes the vertical orientation of influent and effluent within the system of FIG. 3. First, effluent wastewater W is introduced into the aerobic sump 312, the nitrification sump. Liquid from the nitrification sump 312 is removed from the bottom thereof and injected in the filter 314 through the lower port(s) 140. The pressure provided by the liquid coming out of the port 140 is made sufficient to maintain fluidization of the bed material in the filter 314. The fluid in the nitrification sump 312 is aerated, which aeration can occur directly in the nitrification sump 312 or indirectly in a separate aeration sump 312′, the latter of which is shown in FIG. 4. In this first stage 310, ammonia converts to nitrate.
Ammonia-free liquid containing nitrate W1 is, then, transferred to an anaerobic sump 322 of the second stage 320. Liquid from the anaerobic sump 322 is injected into the filter 324 through the lower port(s) 140. The pressure provided by the liquid coming out of the port 140 is made sufficient to maintain fluidization of the bed material in the filter 324. The fluid in the anaerobic sump 322 is not aerated, enabling nitrate in the filter 324 to convert to N2. If further anaerobic filtration is needed to completely convert the nitrate, the portion of the second stage 320 shown in FIG. 4 can be repeated as desired (indicated with the ellipses in FIG. 4) and, as shown in FIG. 3, to transfer effluent Wn from the anaerobic sump 322 to additional repetitive filtration stages.
It is desirable to remove as much solids from wastewater as possible before introducing the wastewater W into the denitrification system. One way to remove such solids is to first send the wastewater W to a solids separator (e.g., a screw press or inclined screen solids separator), in which some of the suspended solids are removed. These solids can be used as a soil amendment if desired. The liquid portion that exits from the solids separator can then be treated with the denitrification system to remove other contaminants.
Removal of nitrogen and odor causing contaminants from wastewater can allow for the reuse of this water for process and waste flushing purposes. Such a practice lowers fresh water usage, which is more environmentally friendly and cost effective than constantly using fresh water.
The flow of water needed to keep the fluidized sand filter systems fluidized often exceeds the overall flow of liquid through the system. As a result, fluidized sand filter systems have traditionally needed to be coupled with additional tankage (sumps) to hold the additional water needed to keep the beds fluidized. This need for additional tankage increases the footprint of the system by as much as two times. Accordingly, there is a need for a system that reduces this extra space for sumps.
Residences, commercial and industrial establishments generate wastewater or sewage. Sewage includes household waste from toilets, baths, kitchens and washing machines as well as wastewater produced from industrial processes like food and chemical production. In a typical metropolitan area all of these sources of wastewater are connected by a network of underground sewers to a sewage treatment plant where the water is processed to eliminate components in the water that could harm the environment. The sewer system includes pipes and pumping stations that move the wastewater from its sources to the waste treatment plant. Some sewer systems also handle storm water runoff. Sewage systems capable of handling storm water are called combined systems. These systems are expensive to operate as they must have the capacity to process surges of storm water along with the normal volume of sewage they treat. As a result, many municipalities have separate sewage and storm water treatment facilities.
Conventional sewage treatment generally includes three stages, generally referred to as primary, secondary and tertiary or advanced treatment. Primary treatment is a process in which raw sewage is screened or treated in holding basins to remove solids. In the holding basin, a scum layer forms and includes, for example, oil, grease, soap, and plastics. The solids and scum are separated from the water and the remaining liquid is, then, further processed. In the secondary treatment step, nutrients, organic constituents, and suspended solids are removed by bacterial organisms in a managed environment. Tertiary or advanced treatment involves the further nutrient and suspended solids removal and disinfection before it is discharged into the environment.
Sewage can also be treated close to where it is generated using septic tanks, biofilters, or aerobic treatment systems. These systems process the wastewater produced from residential, commercial, or agricultural sources at or near the location where they are generated. These systems, which include septic tanks, do not require extensive sewer systems and are, generally, used in locations where access to sewage treatment plants is not practical. Septic tanks employ physical and biological removal of organics similarly to conventional sewage treatment plant but do not have the capacity to handle large surges of wastewater. Because the water in a septic tank is discharged at the same rate it enters the system, the input waste stream can exceed the capacity of the system to process the water before it is discharged. As a result, these systems can and do discharge untreated sewage into the water table. This is a deleterious condition that needs to be eliminated.
Subdivisions and planned urban developments that are not located near sewage treatment plants sometimes use wastewater treatment systems called package plants. Package plants are miniature sewage treatment plants that are configured to handle the needs of a subdivision or an institution, such as a school, from which bathroom and cafeteria wastewater can be processed Like septic tanks, package plants can be hydraulically overloaded during peak loading hours, after lunch is served for example, when large volumes of wastewater enter the system, forcing contaminated water to be discharged before it can be properly processed. Preventing this condition would be desirable.
In municipal areas where large, centralized wastewater treatment facilities are established, sewage can be effectively processed and water discharged into the environment can be controlled and regulated. In rural areas where package plants and septic systems are employed, wastewater discharge into the environment is uncontrolled, largely unregulated and contaminants are routinely discharged into the environment. Preventing such discharge would be desirable.
The same is true for agricultural operations, particularly, large establishments like confined animal feeding operations and dairy farms. There are no standard agricultural wastewater treatment systems on the market. Typically each farming operator retains a wastewater treatment consultant and a custom system is designed to meet their individual needs. Due to the massive amounts of waste created by these facilities and the high cost of municipal-class treatment systems, agricultural waste processing systems often rely on large lagoons to provide secondary and tertiary processing of their waste. Unfortunately these systems are subject to failure due to overflow from heavy rains and leakage from the lagoon basin. Consequently, nutrient-rich water can be discharged into the aquifer and surrounding bodies of water. Preventing such discharge would be desirable.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.